The hierarchy (REF ) was previously presented in [1]} for \(k=1\)  and \(\ell \ge 1\) . Here we present the full range of \(k\)  and \(\ell \)  and show that the maximum number of commutations with \(r^2 \partial _r\)  is exactly \(\ell \)  and which allows us to derive precisely \(\ell +1\)  hierarchies.
